Using rainwater for trees: Why every drop counts

Rainwater is the most natural water source for trees. For millions of years, trees have sustained themselves in this way. However, in many places today, a large portion of precipitation no longer reaches where it is needed: roofs, roads, parking lots, and other sealed surfaces quickly channel rainwater into the sewer system. At the same time, many trees suffer from drought stress. The result: although large amounts of precipitation fall every year, the water is often lacking precisely where it is needed—in the root zone of the trees.

Therefore, rainwater is increasingly becoming a valuable resource. Those who collect rainfall can not only save drinking water but also promote the health of their trees.

Key facts at a glance

• Rainwater is excellent for watering trees.
• It saves drinking water and makes good use of natural rainfall.
• Rain barrels and cisterns help in collecting rainwater.
• Humus, mulch, and healthy soils retain rainwater for longer.
• Even small measures can improve the water supply to trees.
• Rainwater is becoming increasingly important in the context of climate change.

Why rainwater is ideal for trees

For trees, rainwater is the most natural form of irrigation. Unlike many tap waters, rainwater usually contains only small amounts of lime and salts. Furthermore, it often has a temperature closer to natural soil conditions.

Above all, rainwater is available free of charge. It falls directly on site and can often be used with minimal effort. Those who use rainwater save valuable drinking water and utilize a resource that is already available.

Why rain alone is often not enough

At first glance, this sounds contradictory. When it rains, trees should receive sufficient water. In practice, however, this is not always the case.

Especially in recent years, longer periods of drought and short, heavy rainfall events have become increasingly frequent. Large amounts of water fall within a short time. Many soils cannot absorb these amounts of water quickly enough. Some of it runs off the surface and enters the sewer system or waterways. This leads to further problems:

• compacted soils
• sealed surfaces
• Soils low in humus
• restricted root spaces

As a result, significantly less water often reaches the roots than you would expect. You can find more information in this article on the topic. Will there be enough rain for my trees??

Don't just collect: retain rainwater in the ground

When people talk about rainwater harvesting, they often think first of rain barrels or cisterns. However, the question of how to retain water in the ground is at least as important.

Healthy soil acts like a sponge. It absorbs precipitation and slowly releases it back to the plants. The following are particularly important:

• Humus: Humus improves the soil's ability to retain water. Humus-rich soils often remain moist for significantly longer after rain than humus-poor soils.
• Mulch: Mulch protects the soil from direct sunlight and reduces evaporation. At the same time, it promotes soil life and humus formation.
• Soil life: Earthworms, fungi, and microorganisms improve soil structure. This creates cavities that can absorb and store water.
• Avoiding soil compaction: Compacted soils absorb water less effectively. Instead of seeping into the ground, rainwater often runs off the surface.

Collecting rainwater in the garden

Besides storing rainwater in the ground, there are various ways to collect it in a targeted manner:

Rain barrels and rainwater tanks

For many gardens, a rain barrel is the simplest solution. It can be connected to downpipes and collects the water that runs off the roof. The stored water can later be used for irrigation.

Confession

Those who want to store larger quantities of water can use a cistern. Underground storage tanks make it possible to collect rainfall over longer periods and use it during dry spells.

Infiltration basins

Infiltration basins help to direct rainwater directly into the ground on site. This prevents the water from being drained away and makes it available to plants and trees for a longer period.

You can find more technical information about rainwater harvesting in this Article by Baumretter eV.

How much water can be collected?

The sheer quantity involved is often underestimated. A simple example:

Roof area: 100 square meters
Rainfall: 10 millimeters
That already yields approximately 1.000 liters of water.
Even a single summer rain can therefore deliver considerable amounts of water.
The larger the roof area, the greater the potential.

Using rainwater specifically for trees

When rainwater is collected, it should be used as efficiently as possible. The following applies: Better rare and penetrating than frequent and superficial..

Young trees especially benefit from water being released slowly into the root zone. This allows deeper roots to be reached and the water to remain available for a longer period.

Rainwater and climate change

In many regions, periods of drought are becoming more frequent and longer. At the same time, heavy rainfall events are increasing. This creates two opposing problems:

• Too little water over extended periods.
• Too much water in a short period of time.

Therefore, concepts that store rainwater on site and make it usable are gaining in importance.

In this context, cities often refer to the Sponge CityThe goal is to keep precipitation in the ground for as long as possible, instead of draining it away quickly.

This principle can also be implemented in the garden: through humus-rich soils, mulch, infiltration areas and the use of rainwater.